The present invention relates to a method of continuous two-dimensional filtering of discrete m*n data, the data to be processed comprising n lines each containing m data samples, in which method the filtering is performed as successive horizontal and vertical filtering operations and the data is divided for the processing into blocks comprising y lines. The invention also relates to a filter implementing the method.
Two-dimensional discrete m*n data is a set of data samples of variable value, expressed with e.g. 8 data bits, and arranged in ordered pairs of integers m and n in such a way that there are n (1&lt;n&lt;.infin.) lines containing m data samples (1&lt;m&lt;M, where M is a number defined by application needs and technological limits). Public signal processing literature (e.g. D. E. Dudgeon, R. M. Mersereau: Multidimensional Digital Signal Processing. Prentice-Hall, Inc., Englewood Cliffs, N.J. 07632, 1984, pp. 5 to 12, 116 to 118, and J. S. Lim, A. V. Oppenheim: Advanced Topics in Signal Processing. Prentice-Hall, Inc., Englewood Cliffs, N.J. 07632, 1988, pp. 385 to 389) presents practical procedures for continuous two-dimensional filtering of m*n data, for instance overlap-add and overlap-save methods, based on discrete Fourier transformation and derivatives thereof, the methods utilizing the properties of separable systems. These methods process m*n data as blocks, causing detrimental discontinuity in several real-time applications and requiring substantial storage capacity for storing data samples and intermediate results and requiring a transposition of the intermediate results. In conferences and publications, an abundance of solutions implementing a two-dimensional discrete cosine transform have been presented and suggested to be used in HDTV systems, the solutions being based on the above principles.